The present invention relates to a motor case provided with a composite overwrap which protects against case failure due to thermal effects caused by insulator defects or the like, and a method of manufacturing same.
Aluminum has become a desirable material for use in motor cases due to its light weight and durability under normal firing conditions. It is well known that aluminum can be successfully used for motor cases by employing an insulator, such as a sleeve silica phenolic material or the like, which is bonded to the inside of the case to protect the case from overheating when fired. However, such insulators can become cracked due to, for example, adhesive voids between the insulator and the case which allow the insulator to expand outwardly under pressure from motor firing, thereby exceeding the strain capacity of the insulator material. Cracks in the insulator can result in catastrophic case failure upon motor firing due to degradation in the case strength from case overheating caused by propellant gas flow through the cracked insulator. Case failure can result in serious injury or death to personnel in the vicinity of the case.
Therefore, a need has been created for an aluminum man-rated motor case which will not fail due to thermal effects caused by insulator defects or the like, and thereby will maintain safety for the operator and other personnel. The motor case including the composite overwrap and method of manufacture of the present invention meet this need.